1. Field of the Invention
The present invention generally involves the field of technology pertaining to the centrifugal casting of metals. More particularly, the invention relates to an improved method and apparatus for making metal ingots intended for subsequent hot forging.
2. Description of the Prior Art
It is known to be desirable for cast metal ingots to be subsequently worked, such as hot working process by forging, for the purpose of imparting desirable strength and other structural properties to such ingots. Any subsequent working of the ingot is greatly facilitated if the ingot has been cast with a fine grain and close interdendritic structure. By contrast, ingots having a large grain structure and coarse interdendritic spacing are difficult to work and require additional process steps which are costly in terms of both energy and time.
It is further known that the production of close interdendritic spacing in cast metals requires that the molten metal stock be subjected to rapid solidification, thereby producing a metal crystalline structure characterized by close interdendritic spacing, little microsegregation and extremely fine precipitate size. However, known techniques for producing metal ingots and billets through rapid solidification are generally quite limited in application and use since such techniques are both costly and inefficient.
It is known to make a billet having the above mentioned desirable properties according to conventional techniques. For example, the metal is reduced to powder of very small particle size and thereafter rapidly cooled, either by high pressure inert gas or by impinging the powder onto the cooled copper metal heat sink. Another known method involves casting the metal against the metal sink to form a very thin sheet or ribbon of the metal, which is subsequently ground to make a powder thereof. In either case, the resulting metal powder must be compressed in a container, commonly called a "can". This can, together with its contents, must then be consolidated through hot isostatic pressing and/or extruding. Subsequently, the can must be removed and the billet thus obtained is ready for further hot working. For metals containing strong nitride or oxide formers, most or all of the aforedescribed operations must be carried out in the absence of air, such as within a noble gas atmosphere or vacuum protection. It is easily seen that presently available techniques for the production of billets possessing the greatly enhanced properties imparted by rapidly solidified metals and alloys are cumbersome, time consuming and extremely expensive.
There is presently an urgent need for an economical and efficient method of producing reforging metal stock with enhanced metallurgical properties resulting from rapid solidification.